difference between scaffold and model in Rails

Question

What's the difference between generating a scaffold and generating a model in Rails? What are the advantages/disadvantages of doing either?

Answer 1

When you generate a model, you get a model as well as some related components. One of my favorite ways of explaining topics like this is to actually try it out or encourage others to try it, so if I were to enter the command rails generate model Foo name:string description:text within a Rails project, I would get:

invoke  active_record
  create    db/migrate/20130719012107_create_foos.rb
  create    app/models/foo.rb
  invoke    test_unit
  create      test/unit/foo_test.rb
  create      test/fixtures/foos.yml

The first line invokes Active Record, which basically ties your model to your database. The next line creates what's called a migration file. Migration files contain instructions for altering your database. This first migration file creates the database table called 'foos' and it will also create columns for "name" and "description".

The next line makes the model itself. The model is basically a Ruby class that inherits from Active Record. What this means is that any methods that can be called in Active Record can now be called in your model. The last three lines basically create related test files for your model. If you were using RSpec, spec files would be created instead.

If your Rails application only contained models, you would not have any kind of view that displays information on a page, nor would you have instructions that control the flow of information. Your choices would be to also generate controllers (which in turn generates your views) or to generate a scaffold, which generates your model, views, controller, and writes to your routes.rb file. If I ran rails generate scaffold foo I would get:

invoke  active_record
  create    db/migrate/20130719013307_create_foos.rb
  create    app/models/foo.rb
  invoke    test_unit
  create      test/unit/foo_test.rb
  create      test/fixtures/foos.yml
  invoke  resource_route
   route    resources :foos
  invoke  scaffold_controller
  create    app/controllers/foos_controller.rb
  invoke    erb
  create      app/views/foos
  create      app/views/foos/index.html.erb
  create      app/views/foos/edit.html.erb
  create      app/views/foos/show.html.erb
  create      app/views/foos/new.html.erb
  create      app/views/foos/_form.html.erb
  invoke    test_unit
  create      test/functional/foos_controller_test.rb
  invoke    helper
  create      app/helpers/foos_helper.rb
  invoke      test_unit
  create        test/unit/helpers/foos_helper_test.rb
  invoke  assets
  invoke    coffee
  create      app/assets/javascripts/foos.js.coffee
  invoke    scss
  create      app/assets/stylesheets/foos.css.scss
  invoke  scss
 identical    app/assets/stylesheets/scaffolds.css.scss

To answer your question, the advantage of the scaffold is that it's quick, easy, and everything is preconfigured for you. However, the advantages of generating models independently of scaffolds (and then in turn generating controllers/views where needed and writing your routes.rb file yourself) is that you have a lot more control over your app and how it looks and functions, you avoid unnecessary code, you can employ Behaviour-Driven Development or Test Driven Development, and probably other things that someone else might want to add.

My last bit of advice is: Rails is very user-friendly, so try experimenting yourself. You can undo any generate command with a corresponding destroy command, so for instance rails destroy scaffold Foo would delete all the files generated by rails generate Scaffold Foo name:string description:string, so you don't have to worry about irrevocably messing up a project by experimenting.

Answer 2

Generating a scaffold includes generating a model but also generates

• RESTful routes
• a controller with all actions for RESTful handling of the model
• views needed by the controller
• tests stubs

Scaffolding is a good start for new Rails users.

Answer 3

With

$rails generate scaffold <name>

you can auto-generate a ready to use controller, model, and views with a full CRUD (Create, Read, Update, Delete) web interface. It is way easier and way faster than generating models, but the code it generates is unlikely to be a perfect for your application.

A scaffold is excellent to use when it comes to simple examples, quick mockups or testing.

If you change your mind and decide to use scaffold after already generating the model, you can always run

$rails generate scaffold <name>

It will create all the missing files. Or if you are ot happy with using scaffold, you can always remove it in the following way:

Generate scaffold:

$rails generate scaffold Story

If you migrated your files, perform a rollback:

$rake db:rollback

Destroy or undo scaffold: $rails destroy scaffold Story

Answer 4

New users would most likely be confused by scaffolding as they would not understand how all the components work together. Scaffolding is probably best for experienced users who want a shortcut for work they would typically be repeating.